1. Field of the Invention
The present invention relates to a toner set, a developer set, an image forming apparatus and an image forming method.
2. Description of the Related Art
An image forming apparatus which employs an electrophotographic method, such as a copying machine, a printer, a facsimile device, or a composite of these, comprises: an image bearing member, a charger for uniformly charging the surface of the image bearing member, a developing device for forming an electrostatic latent image on the image bearing member, a developing device for developing the electrostatic latent image on the image bearing member into a toner image, a transfer device for transferring the toner image on the image bearing member, onto a recording medium, and the like. The image forming apparatus described above forms an image on a recording medium by transferring a toner image onto a recording medium as described above by means of respective devices.
Image formation apparatuses of this kind are used not only for monochrome printing, but may also be equipped with a color printing function for forming color images. More specifically, for example, an image forming apparatus such as a one-drum color copying machine or a composite device (MFP) which comprises one photoconductive drum is used. However, when printing a color image on one sheet of paper, an image forming apparatus of this kind based on a one-drum system is required to form an image on a photoconductive drum, which is the image bearing member, for respective developing actions onto the paper of each of the colors of black, yellow, cyan and magenta, and the like. Therefore, a problem has arisen in that the printing speed when performing color printing falls to around ¼ the printing speed when performing monochrome printing. In other words, color printing is problematic in requiring approximately four times as long as monochrome printing. Therefore, there have been requirements to shorten the printing time, in other words, to speed up printing, in an image forming apparatus comprising a color printing function. A tandem-system color image forming apparatus, or the like, is one example of an apparatus which satisfies requirements of this kind.
A color image forming apparatus based on a tandem system is, more specifically, an image forming apparatus which comprises, for example, an intermediate transfer belt for secondary transfer onto a transfer receiving medium, such as paper, after primary transfer of a toner image formed on an image bearing member by an electrophotographic method, and which forms a color image by mutually superimposing toner images of a plurality of colors, such as yellow (Y), magenta (M), cyan (C) and black (K), or the like, on the intermediate transfer belt. In a color image forming apparatus of this kind, in order to mutually superimpose toner images of a plurality of colors, developing devices corresponding to the respective colors are arranged in line following the intermediate transfer belt. A color image is formed by successively transferring the toner images of the four colors of YMCK formed on respective photoconductive drums of the developing devices, onto an intermediate transfer belt (primary transfer). The color image which has been formed on this intermediate transfer belt is transferred onto a transfer receiving material, such as paper, by secondary transfer rollers which are situated facing the intermediate transfer body (secondary transfer). By forming toner images corresponding to the respective color on the respective image bearing members in this way, and then mutually superimposing these toner images to form a color image, a tandem-system color image forming apparatus can achieve high-speed printing.
On the other hand, toner such as that described below can be cited as an example of the toner used in an image forming apparatus which employs an electrophotographic method.
A first example is color toner in which a processed pigment obtained by kneading a magenta pigment made of a polyolefin wax and 2,9-dimethyl quinacridone, with a styrene resin or styrene-acrylic copolymer resin, is dispersed in a binder resin (biding resin) made of a polyester resin.
An example of this kind is toner which uses a quinacridone type pigment that is known as a magenta pigment having excellent color hue, and such toner is expected to display excellent offset resistance (fixing properties) and resistance to wrapping (separability).
Furthermore, a second example is a red toner including a binding resin, a colorant, and a releasant, the toner containing a polyester resin as the main component of the binding resin, containing a naphthol AS pigment as the colorant, and containing an ester wax, such as carnauba wax, as the releasant.
The toner according to this example incorporates carnauba wax, which is known as a wax having excellent toner storage stability (resistance to bleeding), fixing properties, and resistance to adhesion, and such toner can be expected to show excellent color hue and make it possible to maintain stable image quality.